Device for adjusting the stroke of a variable displacement pump to maintain the product of pressure and volume per stroke constant

ABSTRACT

A DEVICE FOR ADJUSTING THE STROKE OF A VARIABLE DISPLACEMENT PUMP TO KEEP THE PRODUCT OF THE PRESSURE AND VOLUME PER STROKE CONSTANT, COMPRISES A FLUID PRESSURE ACTUATED ADJUSTING MEMBER FOR VARYING THE VOLUME PER STROKE OF THE PUMP, THE FLOW OF FLUID TO THE ADJUSTING MEMBER BEING CONTROLLED BY A SPOOL VALVE, AN AUXILIARY MEMBER MOUNTED ON A PIVOT, THE PIVOT BEING CARRIED BY AND MOVABLE WITH THE ADJUSTING MEMBER, THE AUXILIARY MEMBER BEING URGED TO TURN ABOUT THE PIVOT IN ONE DIRECTION BY EQUALISING MEANS SUBJECTING SAID MEMBER TO A REDETERMINED SUBSTANTIALLY CONSTANT MOMENT, THE SPOOL OF THE SPOOL VALVE BEING ADAPTED TO TRANSMIT A FORCE TO THE AUXILIARLY MEMBER PROPORTIONAL TO THE PUMP OUTPUT PRESSURE, THE MOMENT OF SAID FORCE OPPOSING THE MOMENT OF   THE EQUALISING MEMBER, THE MOMENT OF THE FORCE VARYING WITH THE MOVEMENT OF THE PIVOT IN PROPORTION TO THE VOLUME PER STROKE.

Jan .12, 1 971" I SC HL|NKE DEVICE FOR ADJUSTING THE T N E M E MD PN S A ME MW ST HEN IRA M H VFN A W FW oww mm m TE SHm m U L 0 v PUMP TO MAINTAIN T FiledAu g, 20. 19 6s 2 Sheets-Sheet 1 33 Fig- 1 I Inventor: GU HTER SCHLTNKE Jan. 12,1971 e. SCHLINKE 3,554,671 DEVICE. FOR ADJUSTING .THE STROKE OF A VARIABLE DISPLACEMENT PUMP TO MAINTAIN THE PRODUCT OF PRESSURE AND VOLUME PER STROKE CONSTANT Filed Aug. 20. 1968 I 2 Sheets-Sheet 2 Fig.3

' In ventar:

QUNTERSCHUHKE United States. Patent Int. Cl. F04b 29/00, 15/22 US. Cl. 417222 8 Claims ABSTRACT OF THE DISCLOSURE A device for adjusting the stroke of a variable displacement pump to keep the product of the pressure and volume per stroke constant, comprises a fluid pressure actuated adjusting member for varying the volume per stroke of the pump, the flow of fluid to the adjusting member being controlled by a spool valve, an auxiliary member mounted on a pivot, the pivot being carried by and movable with the adjusting member, the auxiliary member being urged to turn about the pivot in one direction by equalising means subjecting said member to a predetermined substantially constant moment, the spool of the spool valve being adapted to transmit a force to the auxiliarly member proportional to the pump output pressure, the moment of said force opposing the moment of the equalising member, the moment of the force varying with the movement of the pivot in proportion to the volume per stroke.

This invention relates to a device for adjusting the stroke of variable displacement pumps to maintain the product of the pump output pressure and the volume per stroke at a preset constant value, the displacement pumps having a pressure actuated adjusting member for varying the volume per stroke.

Such devices otter the possibility of keeping the working capacity of such pumps constant When the speed is constant and the forces on the pumps vary; they are therefore also referred to as capacity regulators.

Devices of the above-mentioned kind are known wherein the adjusting member is acted upon by a set of springs which, above a certain fluid-pressure determining the commencement of the control range, are loaded or relieved of load'to varying degrees by the adjusting member in such manner that the stroke of the adjusting member increases in accordance with a prescribed ratio as the pump pressure rises, and the volume per stroke drops, so that the product of the pump output pressure and the volume per stroke remains constant. The springs are here so selected that their characteristic curve is practically hyperbolic when the relationship between the change in volume per stroke and the distance travelled by the adjusting member is linear or almost linear.

These known devices are not completely satisfactory in that, apart from the cost and ditficulty involved in obtaining a hyperbolic curve that is as accurate as possible, a change in the characteristic capacity curve makes it necessary to change the sets of springs.

The object of the present invention is to eliminate the disadvantages described and to provide an improved device of the kind in question such that, on that one hand, an exact hyperbolic relationship between the pump output pressure and the volume per stroke is ensured and, on the other hand, it is possible readily to vary the characteristic capacity curve.

The invention consists in a device for adjusting the stroke of a variable displacement pump to maintain the product of pump output pressure and volume per stroke at a preset constant value, comprising fluid-pressure-actuated stroke adjusting means displaceable for varying the volume per stroke of the pump, valve means for controlling the application of fluid pressure to said stroke adjusting means, a pivot carried by said stroke adjusting means for displacement therewith, a member mounted for rotational movement about said pivot and adapted to operate said valve means in accordance with said rotational movement, equalising means subjecting said member to a preset substantially constant moment above said pivot tending to rotate said member in one direction, and said valve means being adapted to transmit to said member a force proportional to pump output pressure the moment of said force about said pivot tending to rotate said member in the opposite direction and the length of the moment arm being varied by displacement of said pivot in proportion to the volume per stroke.

The device according to the invention offers the advantage that in each unchanging condition the moment of rotation applied by the valve means to the auxiliary member is constant, that is, equal to a value a.f.p, where ;f is the area of the valve spool subjected to the operating pressure 2 and a is the distance from the pivot member to the point of engagement of the valve spool With the auxiliary member. Since, however, a is proportional to the position of the adjusting member and consequently to the volume per stroke V not only does the product a.f.p remain constant, but it can be said that f.p.V is constant, and the requirement regarding an exact regulation of capacity is met.

In a preferred form of construction, the auxiliary member takes the form of a double-armed lever, one arm of which, cooperating with the spool, is provided with a guide for the pivot member which is attached to the adjusting member, its other arm, cooperating with the equalising member, forming a pivoting arm of substantially constant length b. The disposition of the auxiliary member relatively to the valve spool and the equalising member is here preferably so selected that the valve spool acts on the arm incorporating the guide transversely of this guide and the equalising member acts on the other arm in a direction parallel with the path of movement of the pivot member.

In order also to meet the second requirement, relating to ease in varying the characteristic curve, the magnitude of the forces applied by the equalising member is adjustable. This can be achieved for example by the equalising member including a spring, the force of which is adjustable.

Instead of a spring, a cord loaded with weights can be included in the equalising member. If it is desired to alter the characteristic curve of the spring by remote control, it is advantageous if the equalising member includes a control piston actuable by a fluid medium of variable pressure.

In order that the invention may be more clearly understood, an embodiment thereof will now be described by way of example, reference being made to the accompanying drawings in which:

FIG. 1 shows schematically and in section the side view of a device according to the invention fitted to a reciprocating piston pump;

FIG. 2 shows part of a modified form of the device shown in FIG. 1, and

FIG. 3 shows part of a further modified form of the device shown in FIG. 1.

In FIG. 1, the volume per stroke per revolution of the pump depends upon the stroke H of each individual piston a part 11 of each piston engaging swash-plate 12 about an axis 13. For this purpose there is used an adjusting member 14 which is connected to the swash plate 12 by way of a rod 16 mounted in a ball-joint 15.

The adjusting member 14 incorporates a piston part 19, displaceable in two directions within a cylinder 20 by fluid pressure which enters cylinder 20 by way of connection orifices 17 and 18. A spring 21 presses the adjusting member 14 into the end position illustrated when the pump output pressure p is zero. At this position the volume V per stroke is at its greatest.

The annular space 22 in the cylinder 20 communicates by way of a pipe 23 with a pipe 24 in which the pump output pressure 1 obtains and which is also connected with the orifice 25 of the cylinder 26 of a spool valve 27. The valve 27 includes a spool 28 the cross-sectional area of which has the value 1. The spool 28 opens and closes a passage 29, which communicates with the connection orifice 18 by way of a pipe 30, the connection orifice 18 in turn communicating with the cylinder chamber 61 beneath piston 19.

A further orifice 31 in the cylinder 26 connects the annular space 32 in the cylinder, via a pipe 33, with the atmosphere or with a sump 34 for the pressure medium employed.

The spool 27, by its end 35 projecting from the cylinder 26, presses against an auxiliary member 36 which auxiliary member is in the form of a lever having two arms 37 and 38 and can be swung about a pivot member 39. The pivot member 39 is guided in a slot 40; its perpendicular distance a from the centre line of the valve 27 depends upon the position of the adjusting member 14, since it is firmly connected thereto by way of an adjusting spindle 41 and a slotted bolt 42.

The head 43 of a first dished washer 44, to which a force P is transmitted from the helical spring 45, presses against the end of the lever arm 37. A second dished washer, 46, fitted at that end of the spring 45 remote from the first dished washer, bears by its head 47 against the end of a set screw 48, with the help of which the spring pretension can be varied. The spring force P is applied to the lever arm 37 at a substantially constant perpendicular distance from the pivot member 39 during the swinging movements of the auxiliary member 36 about member 39.

The device according to the invention operates as follows:

When the pump is not working, the pump-pressure p=0. The spring 21 presses the adjusting member 14 into the position illustrated. The moment arm a assumes its greatest value which corresponds to the maximum stroke [1 of the adjusting member 14. Since, in FIG. 1, the ratio H:D where D is the distance between piston centres, is equal to the ratio /1:R where R is the distance between the centre of the swash-plate and the longitudinal axis of the adjusting member, I1 is proportional to the value H and thus to the volume V per stroke and this is thus likewise at a maximum when the pump starts up.

When the pump starts up, a pump output pressure p builds up in the pipe 24. A pressure medium flows through the orifice 25 into the cylinder 26 and applies a force pj where f is the working area of the spool 28 of the valve 27 The force 12. initiates a moment of rotation of the magnitude a.p.f in the auxiliary member 36, which moment balances the moment of rotation P Xb, where P is the force exerted by the equalising member on the lever arm 37 of the auxiliary member 36.

If, as a result of external resistance in the system of which the pump is a part, the pressure in the pipe 24 rises to a value P the moment of rotation a.p.f increases to a value ap This moment increase disturbs the equilibrium between the moments of rotation acting on the auxiliary member 36 and causes the auxiliary member to swing in the anti-clockwise direction.

This swinging movement brings about a displacement of the spool 28 to the left, whereby the passage 29 is uncovered and pressure medium flows into the cylinder chamber 61. The increasing pressure in the cylinder chamber 61 causes an upward movement of the adjusting member 14 and thus a shortening of the swinging arm a to a value 11 The upward movement of the adjusting member continues until the moment of rotation from the force p f acting on the auxiliary member 36 and the value a attains a value which again corresponds to the moment of rotation P b. When this value is reached, the auxiliary member 36 begins to move back again in the clockwise direction, and the spool 28 returns to its initial position. A new condition of equilibrium is then established.

Since the product P Xb is constant for all stationary operating conditions, parity must consequently exist between the products a.p and a p since 1 represents a constant. As a result of the proportionality between a and H or V it is therefore also true that the capacity remains constant if the speed 11 of the swash plate is not altered.

It will be understood that the regulating device according to the invention only begins to respond when the moment of rotation a.p.f assumes a value greater than the moment of rotation P Xb. By altering the amount of P the commencement of regulation can consequently be altered together with the characteristic curve of the pump.

In the event of the pressure in the pipe 24 diminishing, the above-described sequence of events takes place in the reverse direction, the pressure medium contained in the annular gap 22 being enabled to fiow away through the pipe 23, the passage 29, the orifice 31 and the pipe 33 into the sump 34, after displacement of the spool 27.

It is worth mentioning that the double-armed lever constituting the auxiliary member 36 is so shaped that the force P is applied at a point which lies on a line which is perpendicular to the direction of movement of pivot member 39 and passes substantially through the middle of its path of movement. In this way, the lever arm b is kept substantially constant.

Whereas in FIG. 1, the equalising member, providing a counter-force to the force applied by the spool 28 to the auxiliary member 36, operates with a spring, the counter-force in the construction shown in FIG. 2 takes the form of a counter-weight consisting of several discs 49.

This counter-weight is suspended on a cord 51 which passes round a roller and engages in a notch 54 in the auxiliary member 55 by means of a tensioning yoke 52 having a knife-edge 53. In this construction, the auxiliary member is coupled with a spool 58 via a ball-joint 56, 57.

Finally, FIG. 3 shows a further variant of the device shown in FIG. 1, wherein the counter-force is provided by means of a piston 59 which is actuable by a fluid medium and is guided in a cylinder 60. The last-described form of construction otters the advantage that it enables the counter-force to be adjusted by remote control.

What is claimed is:

1. A device for adjusting the stroke of a variable displacement pump to maintain the product of pump output pressure and volume per stroke at a preset constant value, comprising fluid-pressure actuated stroke adjusting means displaceable for varying the volume per stroke of the pump, valve means for controlling the application of fluid pressure to said stroke adjusting means, a pivot carried by said stroke adjusting means for displacement therewith, a double-armed lever mounted for rotational movement about said pivot and adapted to operate said valve means in accordance with said rotational movement, one of the arms of said lever cooperating with said valve means and provided with guide means for said pivot, said valve means acting on said last mentioned arm transversely thereof, equalising means subjecting said lever to a preset substantially constant movement above said pivot tending to rotate said lever in one direction, and the other arm of said lever cooperating with said equalising means to form a moment arm of substantially constant length whereby said valve means transmits to said lever a force proportional to pump output pressure with the moment of said force about said pivot tending to rotate said lever ill a direction parallel to the path of movement of said pivot and the length of said second mentioned arm being varied by displacement of said pivot in proportion to the volume per stroke.

2. A device as claimed in claim 4 wherein the valve means includes a spool the longitudinal axis of the spool extending through the pivot attached to the member in the neutral position of the adjusting member.

3. A device for maintaing the product of the amount of fluid delivered by a pump and the pump output pressure at a preset constant value, comprising fluid-pressureactuated adjusting means displaceable for varying the delivered amount of fluid, valve means mounted in a stationary housing and serving to control the application of fluid pressure to said adjusting means, a pivot carried by said adjusting means for displacement therewith, a member mounted for rotational movement about said movable pivot and adapted to operate said valve means in accordance with that rotational movement, first operating means adapted to transmit to said member a force proportional to pump output pressure with said force being dependent upon the movement of said pivot and said adjusting means, the moment of said force about said pivot tending to rotate said member in one direction, second operating means subjecting said member to a preset substantially constant moment tending to rotate said member in the opposite direction.

4; A device as claimed in claim 3, wherein the memher is in the form of an angle-lever, one of the arms of which cooperates with the first operating means and the pivot attached to the adjusting means, and the other arm of which co-operates with the second operating means and forms a moment arm of substantially constant length.

5. A device as claimed in claim 4, wherein the arm co-operating with the first operating means is provided with a guide for the pivot.

6. A device as claimed in claim 5 wherein the first operating means acts on said one arm incorporating the guide transversely of the latter and the second operating means acts on said other arm in a direction parallel to the path of movement of the pivot.

7. A device as claimed in claim 3 wherein the valve means includes a spool forming the first operating means, the longitudinal axis of the spool extending through the pivot attached to the member in the neutral position of the adjusting member.

8. A device as claimed in claim 7, wherein the adjusting member includes at least two parts adjustably connected together for adjusting the position of the pivot member relative to the spool.

References Cited UNITED STATES PATENTS 2,179,071 11/1939 Wiedmann 103-38 2,283,321 5/1942 Doe et a1. 1031XI 2,932,948 4/1960 Neff et al l03lXI 2,971,498 2/1961 Bloch l031XI 3,302,585 2/1967 Adams et al l03lXI 3,403,628 10/1968 Bobst l03-38 3,407,738 10/196'8 Bosch l03-38XI 3,434,427 3/1969 Smith et a1. l03e38 WILLIAM L. FREEH, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,55%671 Dated January 12, 1971 Inventor (s0 Gunter Schlinke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 13, 1" should be -l--.

Signed and sealed this 27th day of April 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents FORM PO-105D [10-69) u c c 00375.; 

